rust/docs/usage.md

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# Usage
rustc_codegen_cranelift can be used as a near-drop-in replacement for `cargo build` or `cargo run` for existing projects.
Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`prepare.sh` and `build.sh` or `test.sh`).
## Cargo
In the directory with your project (where you can do the usual `cargo build`), run:
```bash
$ $cg_clif_dir/build/cargo.sh build
```
This will build and run your project with rustc_codegen_cranelift instead of the usual LLVM backend.
## Rustc
> You should prefer using the Cargo method.
```bash
$ $cg_clif_dir/build/bin/cg_clif my_crate.rs
```
## Jit mode
In jit mode cg_clif will immediately execute your code without creating an executable file.
> This requires all dependencies to be available as dynamic library.
> The jit mode will probably need cargo integration to make this possible.
```bash
$ $cg_clif_dir/build/cargo.sh jit
```
or
```bash
$ $cg_clif_dir/build/bin/cg_clif -Cllvm-args=mode=jit -Cprefer-dynamic my_crate.rs
```
There is also an experimental lazy jit mode. In this mode functions are only compiled once they are
first called. It currently does not work with multi-threaded programs. When a not yet compiled
function is called from another thread than the main thread, you will get an ICE.
```bash
$ $cg_clif_dir/build/cargo.sh lazy-jit
```
## Shell
These are a few functions that allow you to easily run rust code from the shell using cg_clif as jit.
```bash
function jit_naked() {
echo "$@" | $cg_clif_dir/build/bin/cg_clif - -Cllvm-args=mode=jit -Cprefer-dynamic
}
function jit() {
jit_naked "fn main() { $@ }"
}
function jit_calc() {
jit 'println!("0x{:x}", ' $@ ');';
}
```